Low-cost production of solar cells on flexible substrates using printing or web coating technologies is promising highly cost-efficient alternative to traditional silicon-based solar cells. Recently, solar cells fabricated from alloys of copper (Cu) and indium (In) with selenium (Se) or sulfur (S) have been developed. Such solar cells (known as CIGS cells) have been produced using a variety of approaches, including sputtering, evaporation, and chemical vapor deposition. However, vacuum-based deposition systems such as sputtering and evaporation can only control the stoichiometric ratio of co-deposited materials with high-cost, low-speed processes. This limitation severely impacts production of solar cells where active layer composition must be tightly controlled. For example, the synthesis of a high-performance CIGS active layer is only possible within a narrow ratio of copper to indium and/or gallium. Co-evaporation or co-sputtering of the individual CIGS elements requires controlled coordination of the deposition rates in a manner that is uniform both spatially across a substrate and from run to run. It is difficult to deposit uniform films on large areas using coincident vapor phase processes. Furthermore, deposition processes such as sputtering and evaporation typically result in less efficient materials utilization, as deposited material is also transported from the source target to chamber walls or shields rather than just the substrate.
Thus, there is a need in the art for an alternative route in the fabrication of CIGS active layers that overcomes the above disadvantages.